Pelletier, 16, spent 16 months at the center of a widely publicized custody battle between her family and the state of Massachusetts. She returned to her West Hartford home on June 18.

She was admitted to Yale-New Haven Hospital on Sept. 27 suffering from "serious pain" and gastrointestinal distress, according to a Facebook post by Rev. Patrick Mahoney of the Christian Defense Coalition, who has been acting as a spokesman for the Pelletier family.

Mahoney said Monday that Justina returned home to West Hartford Friday, but was re-admitted to Yale-New Haven Hospital around 2 a.m. Monday morning.

"She's having serious pain and serious GI issues, she was actually in Yale-New Haven a week ago for several days," Mahoney said.

Mahoney said Justina's parents, Lou and Linda Pelletier, are staying with her at the hospital, and her three sisters have been visiting when they're not at work.

After 16 months in the custody of the state of Massachusetts after a disagreement about a medical diagnosis, Justina Pelletier returned home to West Hartford on June 18, 2014.

Lou Pelletier did not respond to a request for comment.

Justina was admitted to Boston Children's Hospital in February 2013 after other doctors treated her and disagreed with the family that the girl's symptoms, including weakness, headaches and abdominal pain, were caused by mitochondrial disease, a diagnosis she received at Tufts Medical Center in 2011.

Doctors at Boston Children's said they thought her symptoms were psychologically induced, and diagnosed Pelletier with somatoform disorder, a mental disorder. Boston Children's Hospital officials reported their suspicions of medical child abuse, and the state then refused to release Pelletier to her parents.

CaptionVideo: Justina Pelletier Speaks Out

From YouTube: Justina Pelletier's plea for her immediate release! #freejustina

From YouTube: Justina Pelletier's plea for her immediate release! #freejustina

CaptionWest Hartford Girl To Remain In Massachusetts State Custody Through Holidays

The custody battle over Justina Pelletier will continue, at least through the holidays. Judge Joseph Johnston postponed his final custody decision until Jan. 10, meaning the teen will remain in Massachusetts state custody.

The custody battle over Justina Pelletier will continue, at least through the holidays. Judge Joseph Johnston postponed his final custody decision until Jan. 10, meaning the teen will remain in Massachusetts state custody.

State officials and a Massachusetts judge eventually reached an agreement that allowed Justina to return home in June, and she appeared to be doing well for several months. The Pelletiers shared photos of Justina going on trips and making Fox News appearances on social media, and she was the guest of honor at a "Sparkling Homecoming Celebration" fundraiser on Aug. 17.

"When Justina was released, her spirits were high, her emotions, everything was wonderful," Mahoney said. "But I think a lot of the people across the country still didn't realize that there were massive physical issues that Justina had to deal with."

Mahoney said that for 16 months, "Justina was basically not treated ... [the] protocol that they had was 180 degrees opposed to what should have been done with her care, so she still has very serious physical issues."

Justina's return home to a "loving, caring environment" has been beneficial, but "returning home was only a starting line, it wasn't the end line," Mahoney said.

Mahoney said it's expected that Justina will remain hospitalized for the next few days, and "I think they're determining the cause of some of these issues and to find out what's the best way to move forward and that's where they're at right now."

The Pelletier family will release more details on Justina's condition "as soon as they have some concrete information," Mahoney said.

Lou Pelletier has vowed to fight the medical and legal community that controlled custody of his daughter in Massachusetts, and Justina traveled to Washington, D.C. on July 16 to advocate for a bill named in her honor.

"Justina's Law," sponsored by U.S. Rep. Michele Bachmann, R-Minn., seeks to, "prohibit Federal funding of any treatment or research in which a ward of the State is subjected to greater than minimal risk to the individual's health with no or minimal prospect of direct benefit."

Laws governing the federal Department of Health and Human Services allow the department to conduct or provide funding for research that involves children who are wards of the state in specific circumstances.

During the custody battle involving the Pelletiers, Justina was for a time a ward of the State of Massachusetts.

Federal law allows research "involving greater than minimal risk and no prospect of direct benefit to individual subjects" only if "the risk represents a minor increase over minimal risk," and the research is likely to yield information that "is of vital importance for the understanding or amelioration of the subjects' disorder or condition."

Lou Pelletier has accused the Massachusetts Department of Children and Families of colluding with Boston Children's Hospital to retain custody of Justina and other children with certain medical conditions for research.

"At no time did Boston Children's conduct research on the patient in question," said Rob Graham, spokesman for Boston Children's Hospital, in a written statement. "The allegations that research was conducted on the patient are baseless and patently false."

Graham said the hospital "has been and continues to be a leader in ethical standards in research to protect children, including those in state custody."

"Justina's Law" has also been taken up by the nonprofit lobbying group Child Protection League Action, which was founded in 2013 in response to a Minnesota anti-bullying bill that the group argued promoted acceptance of LGBTQ individuals.

Lou Pelletier and daughter Jennifer Pelletier were speakers at a fundraiser for the group titled, "The Raging War On Kids, Launching The Resistance," in Minnesota on Sept. 20, alongside Bachmann and conservative columnist Matt Barber.